Processes for preparing polyurea resins are disclosed in the specifications of JP-A-56-135514 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-B-60-32641 (the term "JP-B" as used herein means an "examined Japanese patent publication") and JP-B-64-2601, and processes for preparing polyurethane-urea resins are disclosed in the specifications of JP-A-50-132096, JP-B-61-54812 and U.S. Pat. No. 3,681,290. Various polyamines are used in the preparation of these resins. Examples of aromatic amines conventionally used include toluenediamine, 1,2-, 1,3- or 1,4-diaminobenzene, 4,4'-diaminodiphenylmethane, methylenebis(2-chloroaniline), 4-chloro-3,5-diaminobenzoic isobutyl ester, trimethylenebis(4-aminobenzoate) and 1,4-diamino- 2,3-diphenylbutane.
Examples of aliphatic amines conventionally used include propylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, trimethylhexamethylenediamine and polyalkylenepolyamines.
Of these amine compounds, the aromatic amines are used as the chain lengthening agents of urethane prepolymers or crosslinking agents because they have such properties that the mechanical strength, hardness or heat resistance of the resulting resins can be improved. However, the aromatic amines have a high melting point, and hence the mixing thereof with polyisocyanate compounds must be conducted at a high temperature (approximately from 60.degree. to 100.degree. C.), and curing must also be conducted at a high temperature to accelerate curing.
Among the aliphatic amine compounds, those having a low molecular weight are liquid at ordinary temperature. However, the reaction rate of the amine compounds having a low molecular weight with polyisocyanates is rapid, and it is not preferred that the amine compounds are used to obtain curable resins which require flexibility. Among the aliphatic amines, conventional polyalkylenepolyamines can be used to prepare curable resins ranging from resins having flexibility to resins having a high hardness. Accordingly, they are used as starting materials for polyurea resins and curing agents for urethane prepolymers. However, they must have crystallizability at ordinary temperature, the mixing thereof must be conducted at a high temperature because of high viscosity, and curing must be conducted at a high temperature. Further, the resulting curable resins have a problem with regard to mechanical properties.